SPACE SHUTTLE MISSION 51-L: THE SEARCH FOR A CAUSE

By Michael SchrageBy Michael SchrageJanuary 31, 1986

The key to unlocking the mystery of the Challenger disaster may rest with a powerful but obscure computer language that will process virtually all of the raw data sent by the ill-fated space shuttle on its 74-second flight late Tuesday morning.

"It's about the only way we have here of finding out what happened," said Jim Mizell, a spokesman at the National Aeronautics and Space Administration's Kennedy Space Center in Florida.

The language that runs the shuttle's launch processing system, the computer-controlled overseer of the entire launch sequence, is called GOAL, for ground operational applications language. Initially developed by NASA in the early 1970s, GOAL has become the computational cornerstone of the shuttle program.

GOAL-programmed computers track and record everything from the equipment that loads fuel into the shuttle to the myriad sensors providing an up-to-the-millisecond pulse of the shuttle's temperatures, pressures, voltages, valve positions and hundreds of other variables.

NASA technicians and engineers use GOAL to simulate shuttle launch and flight conditions for testing purposes as well as to program the shuttle for flight.

"It's a very large language that allows engineers and technicians to develop applications programs into the computers," Mizell said. For example, "an engineer can use GOAL to write a program that opens and controls valves in a propulsion unit."

But GOAL is also the heart of NASA's efforts to monitor the shuttle in flight.

Upon launch, the shuttle's telemetry system -- a "nervous system" of sensors and computer technology that tracks vital functions -- beams data to ground control where it is simultaneously recorded and processed by computers. Over a million bits of computer information are sent to Earth each second.

"The data that is telemetered back is GOAL-compatible," said Mizell, a telemetry expert for NASA's Apollo moon-landing program, "and it is sent to the computers in the Cape Canaveral firing room."

The computers at Cape Canaveral, using GOAL, transform the raw data into pictures on video screens. Technicians monitoring propulsion units would see up-to-the-second data about the rate of fuel flow; engineers tracking the shuttle's electrical systems might check which switches are on or off.

"It personalizes the data for the technician," Mizell said.

At the same time, the computers are matching data from the shuttle with GOAL programs already in the computers. It means comparing "real time" data from the shuttle to "expected" data.

If the real time data is outside what NASA engineers call the "envelope" of acceptable expected data, the computer screen is supposed to flash a warning.

That did not happen Tuesday morning when Challenger exploded after liftoff.

NASA investigators now face the task of sifting through hundreds of millions of bits of Challenger data, including prelaunch information, to try to figure out what happened.

Only 10 to 15 percent of all of Challenger's telemetry data -- the most important functions -- was being processed by launch processing system computers at Cape Canaveral and elsewhere. The balance is expected to be scrutinized to help fit the missing pieces in the Challenger puzzle.

NASA engineers and computer software specialists will be checking whether there were errors in one or more of the GOAL programs that monitored the fuel tanks, main engines, solid rocket boosters or other vital shuttle systems.

Scientists also will be trying to change the variables that determined the size of the software "envelopes" on the chance that one or more envelopes allowed for too great a margin of error.

"We learned early on that those envelopes are not easy to define," Mizell said.

It is also possible, one software expert who asked not to be named said, that the shuttle software could not cope with something unexpected that triggered the explosion.

"We learned that after engine start it's a whole new ball game and that you could possibly come up with 1,000 different conditions you could find the vehicle and propulsion system in," then-shuttle project engineer Gene Thomas said in 1984 after an aborted Discovery shuttle launch. "Going into it, we were thinking our procedures were so good that we could click things right off."

Now, hundreds of NASA and contractor scientists must count on their programming abilities to dig through the Challenger data to see if they can discover, recreate or simulate precisely what caused the shuttle to explode.